Convective growth of cyclotron harmonic waves on a bounded coaxial electron beam.

Abstract

Analysis and numerical evaluations are presented for the spatial growth of small-signal modified electron Bernstein waves that stand radially and propagate axially along a beam-filled coaxial waveguide. It is shown that these waves, when coupled strongly to fields of an electromagnetic ${\mathrm{TE}}_{11}$ mode in the interior cylindrical waveguide of this configuration, can make possible an amplifier of cyclotron harmonic waves that would possess several unique properties. In particular, millimeter wavelength amplifiers based on this interaction would require neither high magnetic fields nor high electron beam voltages, and thus would not require the bulky superconducting magnets and highly insulated high voltage power supplies usually associated with fast-wave gyro devices. The analysis extends prior work on interactions of this type, including in the calculations simultaneous contributions from more than one term in the infinite series dispersion relation. Effects of finite axial beam velocity spread on the gain and bandwidth characteristics of the interactions are also calculated, thereby accounting for the irreducible velocity spreads attributable to space charge potential depression on the beam.